This invention relates to wound coverings.
In particular, it relates to the wound coverings which comprise two layers, one is a polyurethane resin film which has good moisture permeability, and the other is a sheet of biopolymeric materials, which is effective for growth of tissue cell as an artificial skin.
The properties necessary to wound coverings are 1) adhesion, 2) flexibility, 3) durability, 4) easy handling, 5) preservation, 6) sterile filtration, 7) compatibility with cells, 8) blood stanching, 9) water-vapor permeability and so on.
However, it is the defect for the conventional wound coverings that they satisfy some properties, but they do not satisfy the other properties among those described above.
For example, a sheet consisted of only biopolymeric materials almost lacks flexibility and sterile filtration. In the case of worse flexibility, the sheet lacks adhesion property at a wound surface, and some of such sheets almost lack preservation property, and cannot be handled easily. And also in the case of worse sterile filtration, it is necessary to apply cream containing antibacterial agent every 2 or 3 days to diseased part. This work is very troublesome for nurse and very painful for patient.
On the other hand, a laminated sheet of a biopolymeric material sheet and a silicone film has a poor water-vapor permeability, and is in danger to store exudate under the covering. It is possible to make such a laminated sheet thinner in order to improve these defects. But, a thinner sheet lacks easy handling.
Generally, a lot of exudate is generated at the first stage of using of a wound covering. A laminate sheet is used to be made holes mechanically in it in order to drain the exudate. But, when the generation of the exudate becomes little, the holes are clogged by solidification of the exudate. Therefore, after the clogging of the holes, the sheet is necessary to have good water-vapor permeability. For example, in the case of a burn injury, water-loss by evaporation from a wound is stated to be 300 g H.sub.2 O/m.sup.2 .multidot.24 hrs in the first degree burn, 4300 g H.sub.2 O/m.sup.2 .multidot.24 hrs in the second degree burn, 3400 g H.sub.2 O/m.sup.2 .multidot.24 hrs in the third degree burn. (L. O. Lamke Burns. 3 p 159-165).
A silicone-resin film used as a wound covering, for example, does not have sufficient property of water-vapor permeability, because of its low value of water-vapor permeability, 1000 1700 H.sub.2 O/m.sup.2 .multidot.24 hrs. Therefore, wound covering has not been provided until now, which has a water-vapor permeability sufficient for a large amount of evaporation mentioned above in addition to good flexibility, durability, and easy handleability.
The present inventors have made studies for solving the problems in the conventional sheet which consists of only biopolymeric materials and laminate sheet thereof, i.e., for providing a wound covering which is excellent in 1) adhesion, 2) flexibility, 3) durability, 4) easy handling, 5) preservation, 6) sterile filtration, 7) compatibility with cells, 8) blood stanching as well as 9) water-vapor permeability. As a result of the studies, the present inventors have found that a laminate comprising a specific polyurethane film and a sheet of biopolymeric materials is sufficient for the purpose, and based on this finding the present invention has been accomplished.